土木工程毕业论文外文翻译

土木工程毕业论文外文翻译外文翻译学生姓名邓志望学号0701010304专业班级07级土木工程03班指导教师谭皓职称副教授毕业论文成绩BuildingconstructionconcretecrackofpreventionandprocessingAbstractThecrackproblemofconcreteisawidespreadexistencebutagaindifficultinsolveofengineeringactualproblem,thistextcarriedonastudyanalysistoalittlebitfamiliarcrackproblemintheconcreteengineering,andaimatconcretethecircumstanceputforwardsomeprevention,processingmeasure.Keyword:ConcretecrackpreventionprocessingForewordConcrete'sising1kindisanticipatebythefreestonebone,cement,waterandothermixturebutformationoftheinadditionmaterialofqualitybrittlenessnotandallmaterial.Becausetheconcreteconstructiontransformwithoneself,controletc.aseriesproblem,hardenmodelofintheconcreteexistencenumeroustinyhole,spiritcaveandtinycrack,isexactlybecausethesebeginningstartblemishofexistencejustmaketheconcretepresentonesomenotandallthecharacteristicofquality.Thetinycrackisakindofharmlesscrackandacceptconcreteheavy,defendShenandalittlebitotherusefunctionnotacreationtoendanger.Butaftertheconcretebesubjectedtolotuscarry,differenceintemperatureetc.function,tinycrackwouldcontinuouslyofexpandwithconnect,endformationwecanseewithouttheaidofinstrumentsofmacroviewthecrackbealsothecrackthattheconcreteoftensayintheengineering.ConcretebuildingandGoupieceusuallyalltakesewertomakeof,becauseofcrackofexistenceanddevelopmentusuallymakeinnerpartofreinforcingbaretc.materialcreationdecay,lowerreinforcedconcretematerialofloadingability,durableandanti-Shenability,influencebuildingofexternalappearance,servicelife,severitywillthreatarrivepeople'slifeandpropertysafety.Alotofallofcrashofengineeringsisbecauseoftheunsteadydevelopmentofthecrackwiththeresultthat.Modernagescienceresearchwithagreatdealofoftheconcreteengineeringpracticecertificate,intheconcreteengineeringcrackproblemisineluctable,alsoacceptableincertainlyofthescopejustneedtoadoptvalidofmeasurewillitendangerdegreecontrolatcertainofscopeinside.Thereinforcedconcretenormisalsoexplicitprovision:Somestructureatplaceofdissimilarityundertheconditionallowexistencecertainthecrackofwidth.Butatunderconstructionshouldasfaraspossibleadoptavalidmeasurecontrolcrackcreation,makethestructuredon'tappearcrackpossiblyorasfaraspossibledecreasecrackofamountandwidth,particularlywanttoasfaraspossibleavoidharmfulcrackofemergence,insureengineeringqualitythus.Concretecrackcreationofthereasonbealotofandhavealreadytransformedtocauseofcrack:Suchastemperaturevariety,constringency,inflation,theasymmetrysinktosinketc.reasoncauseofcrack;Haveoutsidecarrythecrackthatthefunctioncause;Protectedenvironmentnotappropriatethecracketc.causedwithchemicaleffect.Wantdifferentiationtotreatintheactualengineering,work°outaproblemaccordingtotheactualcircumstance.Intheconcreteengineeringthefamiliarcrackandtheprevention1.StemSuocrackandpreventionStemtheSuocrackmuchappearaftertheconcreteprotectbeoverofaperiodoftimeorconcretesprinkletobuildtocompletebehindofaroundaweek.InthecementsyruphumidityofevaporatewouldcreationstemSuo,andthiskindofconstringencyiscan'tnegative.StemSuocrackofthecreationbemainisbecauseofconcreteinsideoutsidehumidityevaporatedegreedissimilaritybutcausetotransformdissimilarityofresult:Theconcreteissubjectedtoexteriorconditionofinfluence,surfacehumiditylossleadquick,transformbigger,innerpartdegreeofhumidityvarietysmallertransformsmaller,biggersurfacestemtheSuotransformtobesubjectedtoconcreteinnerpartcontrol,creationmorebigpullshoulddintbutcreationcrack.Therelativehumidityismorelow,cementsyrupbodystemSuomorebig,stemtheSuocrackbemoreeasycreation.StemtheSuocrackismuchsurfaceparallellinesformorthenetshallowthincrack,widthmanybetween0.05-0.2mm,theflatsurfacepartmuchseeinthebigphysicalvolumeconcreteandfollowitmoreinthinnerbeamplankshorttodistribute.StemSuocrackusuallytheanti-Shenofinfluenceconcrete,causethedurableoftherusteclipseinfluenceconcreteofreinforcingbar,underthefunctionofthewaterpressuredintwouldcreationthewaterpowersplitcrackinfluenceconcreteofloadingdintetc..ConcretestemtheSuobemainwithwaterashoftheconcreteratio,thedosageofthecomposition,cementofcement,gathertoanticipateofthedosageofthepropertyanddosage,inadditionetc.relevant.Mainpreventionmeasure:Whilebeingtochoosetousetheconstringencyquantitysmallercement,generallowhotwatermireandpowderashfromstovecementintheadoption,lowerthedosageofcement.TwoisaconcreteofstemtheSuobesubjectedtowaterashratioofinfluencemorebig,waterashratiomorebig,stemSuomorebig,sointheconcretematchtheratiothedesignshouldasfaraspossiblecontrolgoodwaterashratioofchoosetouse,theChanaddinthemeantimeaccommodationofreducewater.Threeisstrictcontrolconcretemixblendwithunderconstructionofmatchratio,useofconcretewaterquantityabsolutecan'tbiginmatchratiodesigngivesettleofusewaterquantity.Fouristheearlierperiodwhichstrengthenconcretetoprotect,andappropriateextensionprotectofconcretetime.Winterconstructionwanttobeappropriateextensionconcreteheatpreservationtooverlaytime,andTu2Shuaprotecttoprotect.Fiveisaconstitutiontheaccommodationisintheconcretestructureoftheconstringencysew.2.TheSuconstringencycrackandpreventionSuconstringencyistheconcreteisbeforecondense,surfacebecauseoflosewaterquickerbutcreationofconstringency.TheSuconstringencycrackisgeneralatdryheatorstrongwindtheweatherappear,crack'smuchpresentinginthecenterbreadth,bothendsbeinthecenterthinandthelengthbedifferent,witheachothernotcoherentappearance.Shortercrackgenerallong20-30cm,thelongercrackcanreachtoa2-3m,breadth1-5mm.Itcreationofmainreasonis:TheconcreteiseventuallyalmosthavingnostrengthorstrengthbeforetheNingverysmall,perhapsconcretejusteventuallyNingbutstrengthveryhour,besubjectedtoheatorcomparestrongwinddintofinfluence,theconcretesurfacelosewatertoleadquick,resultininthecapillarycreationbiggernegativepressbutmakeaconcretephysicalvolumesharplyconstringency,butatthistimethestrengthofconcreteagaincan'tresistitsconstringency,thereforecreationcracked.TheinfluenceconcreteSuconstringencyopenthemainfactorofcracktohavewaterashratio,concreteofcondensetime,environmenttemperature,windvelocity,relativehumidity...etc..Mainpreventionmeasure:OneischoosetousestemtheSuovaluesmallerhigherHuosoursaltoftheearlierperiodstrengthorcommontheHuosourbrinemire.Twoisstrictthecontrolwaterashratio,theChanaddtoefficientlyreducewatertoincrementthecollapseofconcretefalladegreeandwitheasy,decreasecementandwaterofdosage.Threeistosprinklebeforebuildingconcrete,waterbasiclevelandtemplateeventosoakthrough.Fourisintimetooverlaytheperhapsdampgrassmatoftheplasticsthinfilm,hempsliceetc.,keepconcreteeventuallybeforetheNingsurfaceismoist,perhapsspraytoprotectetc.tocarryonprotectintheconcretesurface.Fiveisintheheatandstrongwindtheweathertowanttoestablishtohidesunandblockbreezefacilities,protectintime.3.SinktosinkcrackandpreventionThecreationwhichsinktosinkcrackisbecauseofthestructurefoundationsoilqualitynotandevenly,loosesoftorreturntofillsoildishonestorsoakinwaterbutresultintheasymmetrysinktodeclinewiththeresultthat;Perhapsbecauseoftemplatejustdegreeshortage,thetemplateproppeduptooncebeapartfrombigorpropupbottomloosemoveetc.tocause,especiallyatwinter,thetemplatepropupatjellysoilup,jellythesoilturnjellyempresscreationasymmetrytosinktodeclineandcauseconcretestructurecreationcrack.Thiskindcrackmanyisdeepenterorpiercethroughsexcrack,italignmenthavesomethingtodowithsinkingtosinkacircumstance,generalfollowwithgroundperpendicularorpresent30°s-45°Capedirectiondevelopment,biggersinktosinkcrack,usuallyhavecertainofwrong,crackwidthusuallywithsinktodeclinequantitydirectproportionrelation.Crackwidthundertheinfluenceoftemperaturevarietysmaller.Thefoundationaftertransformstabilitysinktosinkcrackalsobasictendinstability.Mainpreventionmeasure:Oneisrightnessloosesoftsoil,returntofillsoilfoundationaconstructionattheupperpartstructurefrontshouldcarryonnecessityofHangsolidwithreinforce.Twoisthestrengththatassurancetemplateisenoughandjustdegree,andpropupfirm,andmakethefoundationbesubjectedtodinteven.Threeiskeepconcretefromsprinkleinfusingthefoundationintheprocessissoakbywater.Fouristimethattemplatetoredowntocan'tbetooearly,andwanttonoticetodismantleamoldorderofsequence.Fiveisatjellysoiltoptaketoestablishtemplatetonoticetoadoptcertainofpreventionmeasure.4.TemperaturecrackandpreventionTemperaturecrackmuchtheoccurrenceisinbigsurfaceordifferenceintemperaturevarietyofthephysicalvolumeconcretecomparetheearthareaoftheconcretestructure.Concreteaftersprinklingtobuild,inthehardeningtheprocess,cementwaterturnacreationagreatdealofofwaterturnhot,.(bethecementdosageisinthe350-550kg/m3,eachsignsquarethericeconcretewillreleaseacaloriesof17500-27500kJandmakeconcreteinternalthusthetemperaturerisetoreachto70℃orsoevenhigher)Becausethephysicalvolumeofconcretebemorebig,agreatdealofofwaterturnhotaccumulateattheconcreteinnerpartbutnoteasysendforth,causeinnerpartthetemperaturehoick,buttheconcretesurfacespreadhotmorequick,soformationinsideoutsideofbiggerdifferenceintemperature,thebiggerdifferenceintemperatureresultininnerpartandexteriorhotthedegreeofthebulgecoldSuodissimilarity,makeconcretesurfacecreationcertainofpullshoulddint.Whenpullshoulddintexceedtheanti-ofconcretepullstrengthextremelimit,concretesurfacemeetingcreationcrack,thiskindofcrackmuchoccurrenceaftertheconcreteunderconstructionperiod.Intheconcreteofunderconstructionbedifferenceintemperaturevarietymorebig,perhapsisaconcretetobesubjectedtoassaultofcoldwaveetc.,willcauseconcretesurfacethetemperaturesharplydescend,butcreationconstringency,surfaceconstringencyoftheconcretebesubjectedtoinnerpartconcreteofcontrol,creationverybigofpullshoulddintbutcreationcrack,thiskindofcrackusuallyjustinmoreshallowscopeoftheconcretesurfacecreation.Thealignmentofthetemperaturecrackusuallynonesettleregulation,bigareastructurethecrackoftenmaneuverinterleave;Thesizebiggerstructureofthebeamplanklength,thecrackrunparallelwithshortsidemore;Thoroughwithpiercethroughsexoftemperaturecrackgeneralandshortsidedirectionparallelismorcloseparallelism,crackalonglongsidecentthesegmentappear,inthecentermoreairtight.Crackwidththesizebedifferent,besubjectedtotemperaturevarietyinfluencemoreobvious,wintercomparebreadth,summermorenarrow.Theconcretetemperaturecrackthattheheatinflationcauseisusuallyinthecenterthethickbothendsbethin,butcoldSuocrackofthickthinvarietynottooobvious.Theemergenceofthethiskindcrackwillcausetherusteclipseofreinforcingbar,thecarbonizationofconcrete,theanti-jellywhichlowerconcretemelt,anti-tiredandanti-Shenabilityetc..Mainpreventionmeasure:Oneisasfaraspossiblechoosetouselowhotormediumhotwatermire,likemineralresiduecement,powderashfromstovecement...etc..Twoisadecreasecementdosage,cementdosageasfaraspossiblethecontrolisinthe450kg5mmorsosandmatalayerorusageasphaltetc.materialTu2Shua.13istostrengthenconcretetoprotect,theconcreteaftersprinklebuildusemoistgrassLianintime,hempslice'setc.overlay,andattentionsprinklewatertoprotect,appropriateextensionprotecttime,assurancetheconcretesurfacebeslow-movingcooloff.Atthecoldseason,concretesurfaceshouldconstitutionheatpreservationmeasure,inordertopreventcoldwaveassault.14istheallocationbealittleamountintheconcreteofreinforcingbarperhapsaddfibermaterialconcreteoftemperaturecrackcontrolatcertainofscopeinside.5.CrackandpreventionthatthechemicalreactioncauseAlkalibone'santicipatingthecrackthatreactioncrackandreinforcingbarrusteclipsecauseisthemostfamiliarinthereinforcedconcretestructureofbecauseofchemicalreactionbutcauseofcrack.Theconcreteblendafuturereunioncreationsomealkalescenceion,theseionwithsomeactivitytheboneanticipatecreationchemicalreactionandabsorbsurroundingsenvironmentinofwaterbutthephysicalvolumeenlarge,makeconcretecrisploose,inflationopencrack.Inthiskindofcrackgeneralemergenceconcretestructureusageperiod,onceappearverydifficultremediable,soshouldatunderconstructionadoptvalidthemeasurecarryonprevention.Mainofpreventionmeasure:Whilebeingtochoosetoanticipatewiththealkaliactivitysmallfreestonebone.Twoistheinadditionwhichchoosetouselowlyemirewithlowalkaliorhavenoalkali.ThreeistheChanwhichchoosetouseaccommodationwithanticipatetorepressanalkalibonetoanticipatereaction.Becausetheconcretesprinkletobuild,flapDaobadperhapsisareinforcingbarprotectionlayerthinner,theharmfulmaterialgetintoconcretetomakereinforcingbarcreationrusteclipse,thereinforcingbarphysicalvolumeoftherusteclipseinflation,causeconcretebulgecrack,thecrackofthiskindtypemuchisacracklengthways,followthepositionofreinforcingbarappear.Usuallyofpreventmeasurefromhave:Oneisassurancereinforcingbarprotectionthethicknessofthelayer.Twoisaconcreteclasstogotogetherwithtowantgood.ThreeisaconcretetosprinkletonoteandflapDaoairtightsolid.FourisareinforcingbarsurfacelayerTu2Shuaantisepsiscoating.CrackprocessingTheemergenceofthecracknotonlywouldinfluencestructureofwholewithjustdegree,returnwillcausetherusteclipseofreinforcingbar,accelerationconcreteofcarbonization,lowerdurableandanti-ofconcretetired,anti-Shenability.Thereforeaccordingtothepropertyofcrackandconcretecircumstancewewantdifferentiationtotreat,intimeprocessing,withassurancebuildingofsafetyusage.Therepairmeasureoftheconcretecrackismaintohavethefollowingsomemethod:Surfacerepairmethod,infusesyrup,theQiansewmethod,thestructurereinforceamethod,concretedisplacementmethod,electricitychemistryprotectionmethodandimitatetolivingfromhealmethod.Surfacerepairthemethodbeakindofsimple,familiarofrepairmethod,itmainbeapplicabletostabilityandtostructureloadingtheabilitydon'thavethesurfacecrackofinfluenceanddeepentercrackofprocessing.Theprocessingmeasurethatisusuallyisasurfaceincrackdauberycementsyrup,thewreathoxygengummireoratconcretesurfaceTu2Shuapaint,asphaltetc.antisepsismaterial,atprotectionofinthemeantimeforkeepingconcretefromcontinueundertheinfluenceofvariousfunctiontoopencrack,usuallycanadoptionthesurfaceincrackgluetostickglassfiberclothetc.measure.1,infusesyrup,theQiansewmethodInfuseasyrupmethodmaintheconcretecrackbeenapplicabletohaveinfluenceorhavealreadydefendShenrequesttothestructurewholeofrepair,itismakeuseofpressureequipmentsgumknotthematerialpressintothecrackofconcrete,gumknotthematerialhardenbehindandconcreteformationonebewhole,thusreinforceofpurpose.Theincommonusegumknotmaterialhasthecementthesyrup,epoxy,AJiCXisouresterandgatherammoniaestertoequalizetolearnmaterial.TheQiansewamethodisthatthecrackbeakindofmostincommonusemethodin,itusuallyisfollowthecrackdigslot,theQianfillSuintheslotorrigidwatermaterialwithattainclosingcrackofpurpose.TheincommonuseSumaterialhasPVCgummire,plasticsointment,theDJirubberetc.;Incommonuserigidwatermaterialisthepolymercementsandsyrup.2,thestructurereinforceamethodWhenthecrackinfluencearriveconcretestructureoffunction,willconsiderationadopttoreinforceamethodtocarryonprocessingtotheconcretestructure.Thestructurereinforcemediumincommonusemainhavethefollowingafewmethod:Thepieceofenlargementconcretestructureineveryaspectaccumulate,outsidetheCapedepartmentoftheGoupiecepacktypesteel,adoptionprepareshouldthedintmethodreinforce,gluetosticksteelplatetoreinforce,increasetoestablishfulcrumtoreinforceandjettheconcretecompensationreinforce.3,concretedisplacementmethodConcretedisplacementmethodisprocessingseveritydamageconcreteofakindofvalidmethod,thismethodbefirstwilldamageoftheconcretepickandgetridof,thenagaindisplacementgointonewofconcreteorothermaterial.Theincommonusedisplacementmaterialhave:Commonconcreteorthecementsandsyrup,polymerorchangesexpolymerconcreteorsandsyrup.4,theelectricitychemistryprotectionmethodTheelectricitychemistryantisepsisistomakeuseofinflictionelectricfieldinliethequalityofelectricitychemicaleffect,changeconcreteorreinforcedconcretetheenvironmentappearanceoftheplace,thebluntnessturnreinforcingbartoattainthepurposeofantisepsis.Cathodeprotectionmethod,chlorinesalt'swithdrawingamethod,alkalescencetorecoveramethodisachemistryprotectionmethodinthreekindsofincommonusebutvalidmethod.Theadvantageofthiskindofmethodisaprotectionmethodundertheinfluenceofenvironmentfactorsmaller,applyreinforcingbar,concreteoflong-termantisepsis,sincecanusedforcrackstructurealreadycanalsousedfornewsetupstructure.5,imitatetolivingfromlegalmoreImitatetolivingfromhealthemethodbeakindofnewcracktreatment,itsmimicrylivingcreatureorganizationsecreteacertainmaterialtowardssufferingwoundpartauto,butmakethewoundparthealoffunction,joinsomeandspecialcomposition(suchascontaintoglueknotoftheliquidXinfiberorcapsule)intheconcreteofthetraditionthecomposition,atconcreteinnerpartformationtheintelligencetypeimitatetolivingfromhealnervenetworksystem,betheconcreteappearcracksecreteapartsofliquidXinfibercanmakethecrackre-heal.ConclusionThecrackiswidespreadintheconcretestructureexistenceofakindofphenomenon,itofemergencenotonlywilllowertheanti-Shenofbuildingability,influencebuildingofusagefunction,andwillcausetherusteclipseofreinforcingbar,thecarbonizationofconcrete,lowerthedurableofmaterial,influencebuildingofloadingability,sowanttocarryontotheconcretecrackearnestresearch,differentiationtreat,adoptionreasonableofthemethodcarryonprocessing,andatunderconstructionadoptvariousvalidofpreventionmeasuretopreventioncrackofemergenceanddevelopment,assurancebuildingandGoupiecesafety,stabilitywork.From《CANADIANJOURNALOFCIVILENGINEERING》建筑施工混凝土裂缝的预防与处理混凝土的裂缝问 题 快递公司问题件快递公司问题件货款处理关于圆的周长面积重点题型关于解方程组的题及答案关于南海问题 是一个普遍存在而又难于解决的工程实际问题，本文对混凝土工程中常见的一些裂缝问题进行了探讨分析，并针对具体情况提出了一些预防、处理 措施 《全国民用建筑工程设计技术措施》规划•建筑•景观全国民用建筑工程设计技术措施》规划•建筑•景观软件质量保证措施下载工地伤害及预防措施下载关于贯彻落实的具体措施 。关键词：混凝土裂缝预防处理前言　　混凝土是一种由砂石骨料、水泥、水及其他外加材料混合而形成的非均质脆性材料。由于混凝土施工和本身变形、约束等一系列问题，硬化成型的混凝土中存在着众多的微孔隙、气穴和微裂缝，正是由于这些初始缺陷的存在才使混凝土呈现出一些非均质的特性。微裂缝通常是一种无害裂缝，对混凝土的承重、防渗及其他一些使用功能不产生危害。但是在混凝土受到荷载、温差等作用之后，微裂缝就会不断的扩展和连通，最终形成我们肉眼可见的宏观裂缝，也就是混凝土工程中常说的裂缝。　　混凝土建筑和构件通常都是带缝工作的，由于裂缝的存在和发展通常会使内部的钢筋等材料产生腐蚀，降低钢筋混凝土材料的承载能力、耐久性及抗渗能力，影响建筑物的外观、使用寿命，严重者将会威胁到人们的生命和财产安全。很多工程的失事都是由于裂缝的不稳定发展所致。近代科学研究和大量的混凝土工程实践证明，在混凝土工程中裂缝问题是不可避免的，在一定的范围内也是可以接受的，只是要采取有效的措施将其危害程度控制在一定的范围之内。钢筋混凝土规范也明确规定：有些结构在所处的不同条件下，允许存在一定宽度的裂缝。但在施工中应尽量采取有效措施控制裂缝产生，使结构尽可能不出现裂缝或尽量减少裂缝的数量和宽度，尤其要尽量避免有害裂缝的出现，从而确保工程质量。　　混凝土裂缝产生的原因很多，有变形引起的裂缝：如温度变化、收缩、膨胀、不均匀沉陷等原因引起的裂缝；有外载作用引起的裂缝；有养护环境不当和化学作用引起的裂缝等等。在实际工程中要区别对待，根据实际情况解决问题。　　混凝土工程中常见裂缝及预防:　　1.干缩裂缝及预防　　干缩裂缝多出现在混凝土养护结束后的一段时间或是混凝土浇筑完毕后的一周左右。水泥浆中水分的蒸发会产生干缩，且这种收缩是不可逆的。干缩裂缝的产生主要是由于混凝土内外水分蒸发程度不同而导致变形不同的结果：混凝土受外部条件的影响，表面水分损失过快，变形较大，内部湿度变化较小变形较小，较大的表面干缩变形受到混凝土内部约束，产生较大拉应力而产生裂缝。相对湿度越低，水泥浆体干缩越大，干缩裂缝越易产生。干缩裂缝多为表面性的平行线状或网状浅细裂缝，宽度多在0.05-0.2mm之间，大体积混凝土中平面部位多见，较薄的梁板中多沿其短向分布。干缩裂缝通常会影响混凝土的抗渗性，引起钢筋的锈蚀影响混凝土的耐久性，在水压力的作用下会产生水力劈裂影响混凝土的承载力等等。混凝土干缩主要和混凝土的水灰比、水泥的成分、水泥的用量、集料的性质和用量、外加剂的用量等有关。　　主要预防措施：一是选用收缩量较小的水泥，一般采用中低热水泥和粉煤灰水泥，降低水泥的用量。二是混凝土的干缩受水灰比的影响较大，水灰比越大，干缩越大，因此在混凝土配合比 设计 领导形象设计圆作业设计ao工艺污水处理厂设计附属工程施工组织设计清扫机器人结构设计 中应尽量控制好水灰比的选用，同时掺加合适的减水剂。三是严格控制混凝土搅拌和施工中的配合比，混凝土的用水量绝对不能大于配合比设计所给定的用水量。四是加强混凝土的早期养护，并适当延长混凝土的养护时间。冬季施工时要适当延长混凝土保温覆盖时间，并涂刷养护剂养护。五是在混凝土结构中设置合适的收缩缝。　　2.塑性收缩裂缝及预防　　塑性收缩是指混凝土在凝结之前，表面因失水较快而产生的收缩。塑性收缩裂缝一般在干热或大风天气出现，裂缝多呈中间宽、两端细且长短不一，互不连贯状态。较短的裂缝一般长20-30cm，较长的裂缝可达2-3m，宽1-5mm.其产生的主要原因为：混凝土在终凝前几乎没有强度或强度很小，或者混凝土刚刚终凝而强度很小时，受高温或较大风力的影响，混凝土表面失水过快，造成毛细管中产生较大的负压而使混凝土体积急剧收缩，而此时混凝土的强度又无法抵抗其本身收缩，因此产生龟裂。影响混凝土塑性收缩开裂的主要因素有水灰比、混凝土的凝结时间、环境温度、风速、相对湿度等等。　　主要预防措施：一是选用干缩值较小早期强度较高的硅酸盐或普通硅酸盐水泥。二是严格控制水灰比，掺加高效减水剂来增加混凝土的坍落度和和易性，减少水泥及水的用量。三是浇筑混凝土之前，将基层和模板浇水均匀湿透。四是及时覆盖塑料薄膜或者潮湿的草垫、麻片等，保持混凝土终凝前表面湿润，或者在混凝土表面喷洒养护剂等进行养护。五是在高温和大风天气要设置遮阳和挡风设施，及时养护。　　3.沉陷裂缝及预防　　沉陷裂缝的产生是由于结构地基土质不匀、松软或回填土不实或浸水而造成不均匀沉降所致；或者因为模板刚度不足，模板支撑间距过大或支撑底部松动等导致，特别是在冬季，模板支撑在冻土上，冻土化冻后产生不均匀沉降，致使混凝土结构产生裂缝。此类裂缝多为深进或贯穿性裂缝，其走向与沉陷情况有关，一般沿与地面垂直或呈30°-45°角方向发展，较大的沉陷裂缝，往往有一定的错位，裂缝宽度往往与沉降量成正比关系。裂缝宽度受温度变化的影响较小。地基变形稳定之后，沉陷裂缝也基本趋于稳定。　　主要预防措施：一是对松软土、回填土地基在上部结构施工前应进行必要的夯实和加固。二是保证模板有足够的强度和刚度，且支撑牢固，并使地基受力均匀。三是防止混凝土浇灌过程中地基被水浸泡。四是模板拆除的时间不能太早，且要注意拆模的先后次序。五是在冻土上搭设模板时要注意采取一定的预防措施。　　4.温度裂缝及预防　　温度裂缝多发生在大体积混凝土表面或温差变化较大地区的混凝土结构中。混凝土浇筑后，在硬化过程中，水泥水化产生大量的水化热，（当水泥用量在350-550kg/m3，每立方米混凝土将释放出17500-27500kJ的热量，从而使混凝土内部温度升达70℃左右甚至更高）。由于混凝土的体积较大，大量的水化热聚积在混凝土内部而不易散发，导致内部温度急剧上升，而混凝土表面散热较快，这样就形成内外的较大温差，较大的温差造成内部与外部热胀冷缩的程度不同，使混凝土表面产生一定的拉应力。当拉应力超过混凝土的抗拉强度极限时，混凝土表面就会产生裂缝，这种裂缝多发生在混凝土施工中后期。在混凝土的施工中当温差变化较大，或者是混凝土受到寒潮的袭击等，会导致混凝土表面温度急剧下降，而产生收缩，表面收缩的混凝土受内部混凝土的约束，将产生很大的拉应力而产生裂缝，这种裂缝通常只在混凝土表面较浅的范围内产生。　　温度裂缝的走向通常无一定规律，大面积结构裂缝常纵横交错；梁板类长度尺寸较大的结构，裂缝多平行于短边；深入和贯穿性的温度裂缝一般与短边方向平行或接近平行，裂缝沿着长边分段出现，中间较密。裂缝宽度大小不一，受温度变化影响较为明显，冬季较宽，夏季较窄。高温膨胀引起的混凝土温度裂缝是通常中间粗两端细，而冷缩裂缝的粗细变化不太明显。此种裂缝的出现会引起钢筋的锈蚀，混凝土的碳化，降低混凝土的抗冻融、抗疲劳及抗渗能力等。　　主要预防措施：一是尽量选用低热或中热水泥，如矿渣水泥、粉煤灰水泥等。二是减少水泥用量，将水泥用量尽量控制在450kg/m3以下。三是降低水灰比，一般混凝土的水灰比控制在0.6以下。四是改善骨料级配，掺加粉煤灰或高效减水剂等来减少水泥用量，降低水化热。五是改善混凝土的搅拌加工工艺，降低混凝土的浇筑温度。六是在混凝土中掺加一定量的具有减水、增塑、缓凝等作用的